The present invention relates generally to a resin composition, and more particularly, to a curing type resin composition.
A resin composition comprising a silicone-modified acrylic resin and a curing agent is widely known as a curing type resin composition. This type of resin composition is suitable for use as a coating material such as a paint, or as a molding material, since the resin composition forms a cured resin with the combined characteristics of heat-resistance, water repellency, weatherability, and high mechanical strength imparted by the modified acrylic resin.
The silicone-modified acrylic resin which composes the resin composition is generally a silicone-graft acrylic resin obtained by copolymerization of polydimethylsiloxane macromonomers having polymerization radical groups. Japanese Laid-Open Patent Application Nos. 154766/1983, 20360/1984 and 126478/1984, for example, disclose that the inclusion of the foregoing silicone-graft acrylic resin in a coating material composition improves such characteristics as water repellency, oil repellency, contamination-resistance and abrasion-resistance. Japanese Laid-Open Patent Application Nos. 156172/1987, 1772/1989, 1773/1989 and 4670/1989 teach using a composition comprising the silicone-graft acrylic resin for application as an antifouling paint. Japanese Laid-Open Patent Application Nos. 151272/1986 and 59672/1987 disclose a high-weatherability paint and a parting agent, both of which contain, as a principal resin component, a silicone-graft acrylic resin composed of polydimethylsiloxane macromonomer, a cross-linking monomer, and a radical-polymerizing monomer.
However, the cross-linking reactivity of the silicone-graft acrylic resin therein is insufficient, since the silicone segments of the branch chains of the silicone-graft acrylic resin have no functional groups. Moreover, according to the Eighth Toryo-Toso Gizyutsu Sogokenkyu Happyokai Preprints, 8, 9 ( 1990), a micro-separated phase in a coating formed from the foregoing compositions was observed between the silicone and acrylic resin portions, such that the characteristics imparted by the silicone component are not therefore exhibited uniformly throughout the coating. Furthermore, due to segmental localization of the silicone, recoating characteristics of the coating composition are not satisfactory, although parting characteristics are improved.
Furthermore, a graft polymer obtained by the copolymerization of a silicone macromonomer, including two or more free functional groups from the alkoxysilyl or silanol groups, with a vinyl monomer is also known as a silicone-modified acrylic resin. Japanese Laid-Open Patent Application No. 275132/1987, for example, discloses that characteristics of weatherability, water repellency, and cross-linking reactivity of this type of graft polymer are satisfactory, and that it is compatible with other resins.
In application of this of silicone-modified acrylic resin, the Si--O--C bonds created in the reaction of the acrylic resin with the hydroxyl group of the curing agent tend to be hydrolyzed; consequently the characteristics imparted by the silicone gradually deteriorate. This is because the reaction of the alkoxysilyl groups and the silanol groups proceeds only wherein there is, in the presence of water, a self-condensation reaction, and a dealcoholate reaction or a dehydrate reaction with a hydroxyl group.